JMHO but I think it's a lot to do with what society as a whole finds acceptable. Since people are largely uninformed about addiction unless it touches their lives intimately or they work in that field, they simply don't understand how intolerable it is. They often don't know the difference between an alcoholic & a normal drinker.
For those of us that were raised by alcoholic parents it's easy to accept it as "normal" because the foundation of our entire lives is built on it in one way or another. Sometimes you simply don't know any better because you haven't been exposed to any better. Lack of education & support.
OTOH - cheaters & abusers are not largely tolerated & those scars are visible & more obvious. No one questions why anyone would leave a relationship with that dysfunction, they wonder why you stayed so long.